1. Field of the Invention
The present invention relates to a transmission system for a tractor, adapted for transmitting power of an engine to axles through a traveling transmission line and also to an externally mounted utility implement through a PTO transmission line.
2. Description of the Related Art
Tractors selectively employ a gear change speed mechanism or an HST (hydrostatic transmission) mechanism as a traveling change speed mechanism, whichever is appropriate. In recent years, however, different types of transmission systems are required to cope with a variety of works. If different types of transmission systems of respectively desired types are to be provided, this results in increase in the types of transmission cases to be prepared therefor, thus leading to disadvantageous cost increase for preparing molds used for casting the cases.
Then, in an attempt to reduce the mold costs, e.g. the Japanese Patent Application “Kokai” No. 2002-127766 (FIGS. 3, 4 and 14) proposed to utilize a case construction which can be used for both the gear type change speed mechanism and the HST change speed mechanism.
More particularly, this transmission system is provided as a “mono-body” vehicle construction comprising an assembly of a clutch housing 7 and a transmission case 9 formed by casting, which are interconnected via a center plate 12. With this construction, however, either the gear change speed mechanism or the HST mechanism needs to be housed within a limited space of a fixed shape formed inside a rear portion of the clutch housing 7. Hence, this construction imposes restriction in the choice of the gear change speed mechanism or the HST mechanism which can be housed within such limited space.